Method of making electrical resistance element



p 1964 "r. M. PLACE, sR., ETAL 3,149,002

METHOD OF MAKING ELECTRICAL RESISTANCE ELEMENT Original Filed March 18, 1957 /NVNTOR$. THoMns M. PLacs 5R.

THOMAS M. PLACE. JR. By 7H5? A TERA/E75 United States Patent 3,149,002 METHOD OF MAKING ELECTRICAL RESISTANCE ELEMENT Thomas M. Place, Sr., Newport Beach, and Thomas M. Place, J12, Costa Mesa, Califi, assiguors to Beckman Instruments, Inc, Fullerton, Caiifi, a corporation of California Original application Mar. 18, 1957, Ser. No. 646,888, now Patent No. 2,950,995. Divided and this application Mar. 4, 1960, Ser. No. 16,624

12 Claims. (Cl. 117-227) This invention relates to methods for making resistance elements for use in electrical circuits and, in particular, to resistance elements which are formed by applying a layer of particular resistance material to an electrically nonconducting high-temperature-resistant base.

This application is a division of our copending application entitled Electrical Resistance Element and Method of Making Same, Serial No. 646,888, filed March 18, 1957, and now Patent No. 2,950,995, which copending application is a continuation-in-part of our application entitled Electrical Resistor and Method of Making the Same, Serial No. 439,650, filed June 28, 1954, now abandoned.

Resistance elements have been made by winding metal wire or ribbon on nonconducting cores or cards. Such wound resistors are characterized by good stability and close control of resistance tolerances. However, such metals are available with only relatively low ohmic resistances and wound resistors are limited in resistance range by this low ohmic resistance and by the minimum size of wire or ribbon that can be drawn and wound economically. ,In. many applications, wound resistors are bent or shaped to particular configurations for use in specific equipment, after being wound. Therefore, the cores of such resistors must be of ductile material and, while such core materials are satisfactory at normal temperatures, such cores may be seriously alTected by the higher temperatures encountered in present day applications which may result in rapid deterioration of the electrical characteristics of the component.

Resistors have also been formed by applying thin metallic films to nonconducting base materials, such as by sputtering or evaporative techniques. Conducting metals with relatively'low ohmic resistances, such as gold, platinum, palladium, nickel, etc., have been used in the manufacture of such resistors. These metals are deposited in exceedingly thin films. For higher resistance values, the film thickness is only slightly greater than the molecular size of the metal, with the resistance characteristic resulting from the small cross-sectional area of .the metal. These thin films deposited on relatively thick base materials are subject to deterioration from electrical currents and from temperature variations as well as from mechanical stresses and abrasion.

Low cost resistance elements are manufactured by depositing carbon and boro-carbon on nonconducting base materials, the ohmic resistances of various forms of carbon being somewhat higher than that of the metals previously referred to. However, such deposited carbon resistance elements have variable and inferior temperature and voltage coefficients of resistivity and have numerous surface irregularities which present difiiculties when used as variable resistance elements. 1

In general, the resistance element produced by the invention is a layer of resistance material comprising a heterogenous mixture of nonconducting material and conducting metals fixed to a nonconducting base with the overall resistance of the element dependent upon therelative proportion of nonconducting material and conducting 3,149,002 Patented Sept. 15, 1964 metal and upon the particular metal or combination of metals utilized in the resistance material. The nonconducting material is ceramic in nature and thelayer is formed by heating the mixture at least to the melting point of the ceramic but not to the melting point of the metals to create a smooth, glassy phase.

It is an object of the invention to provide methods for manufacturing of resistance material of, such methods including the steps of forming a mixture of volatile carrier and finely ground binder and metal, applying a layer of the mixture to a base and firing the base and layer, first to a relatively low temperature for removing the volatiles and organic material from the layer and then to a relatively high temperature for converting the ground binder into a continuous glassy phase without melting the finely ground metal dispersed therein. Another object of the invention is to provide a process for forming such resistance material in which the metal is added to the mixture in solution in the form of metal organic compounds, such as metallic resinates, with the organic compounds being reduced by heating the mixture, resulting in the metal being dispersed throughout the mixture in finely divided form. A further object of the invention is to provide a process for manufacturing such resistance material in which metal-glass mixtures having various resistance characteristics may be prepared and stored indefinitely for subsequent use in the manufacture of individual resistance elements.

The invention also comprises novel steps and procedures. which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawing:

FIG. 1 is an isometric view of apreferred embodiment of the invention which is suitable for use in rotary p'otentiometers;

FIG. 2 is an isometric view'of another embodiment of the invention which is suitable for use in linear potentiometers as Well as for a fixed resistor;

FIG. 3 is an isometric view of another embodiment of the invention having flexible leads for connection into an electrical circuit; and

FIG. 4 is an isometric view of another embodiment of the invention used as a button-type resistor.

In the structure of FIG. 1, a layer 10 of resistance material is fired to a base 11 with electrodes 12, 13 being provided at each end of the layer 10 for connecting it into an electrical circuit. This resistance element may be used as a fixed resistor or may be combined with a rotating contact arm for use as a rotary potentiometer. The base 11 may be of any suitable electrically nonconducting material which will withstand the elevated temperatures used in firing the resistance material. Various ceramic materials are suitable for this use, those having a smooth, fine textured surface and being impervious to moisture and other liquids being preferred. Steatite, fosterite, sintered or fused aluminas and zircon porcelains are examples of preferred materials for forming the base 11.

The electrical conductive electrodes 12, 13 are conventional and may be formed by applying any of the well known conducting silver or other metal pastes over the layer of resistance material and firing the unit to convert the paste to a layer of metal which is firmly attached to the layer of resistance material. Then leads may be connected to the electrodes by suitable means, such as by clamping or by soldering. Alternatively, leads in the form of wire or ribbon may be placed in grooves or openings in the base 11 prior to firing on the layer 10 so that the wire or ribbon will project into the layer and'be adheredthereto during the firing process.

The layer 10 consists of the fused mixture of a nonconducting binder material and metal with traceamounts of certain other materials added when desired. The binder should not absorb moisture and should be resist-- ant to high humidity and fungus and should fuse to a smooth surface, continuous glassy phase on heating to a temperature below the melting point of the metal or metals mixed therewith. It has been found that a ceramic glass is suitable for this purpose and lead borosilicat'e glasses are preferred for use in the invention. The particular composition of the glass utilized is not critical to the practice of'the invention and various changes in the composition of the glasses can be made to alter the fusion temperature, coefficient of thermal expansion, fluidity, solubility, etc., by one familiar with the ceramic arts to provide a particular desired characteristic. The composition of two glasses which have been used in the practice of the invention are given below as illustrative, but are in no way intended to be restrictive on the composition used in the resistance material.

- Glass No. 1

Red lead 74.1 Z inc oxide 5.4 Boric acid 15.9 Flint 1 3.4 Lead oxide .722 Zinc oxide .050 Boric oxide .090 Silica .134

Glass N0. 2

Red lead 67.3. Zinc oxide 5.4 Boric acid -l 17.7 Ultrox 3.8 Flint 15.1 Lead oxide .6570 Zinc oxide .0540 Boric oxide .0898 Silica .1749 Zircon oxide .0239

' While the glass may be produced by any conventional process, it is preferred that it be as homogenous as possible. One method of making a glass includes thorough- 1y mixing a batch of raw materials together while dry,

melting the batch in ceramic crucibles to produce a clear fluid glass, quenching the molten glass by pouring into cold Water, drying the resulting shattered glass and crushing and then grinding it to a very fine powder with .all particles less than about 325 mesh in size. I

The metal or metals used in the mixture are nonreactive and nonoxidizable. The term nonreactive means that the metal will not react with the other components of the mixture" either at room temperature'or a the elevated temperatures required to produce the continuous, glassy finished resistance element. The term nonoxidizable means that the metal does not oxidizei'n a normal atmosphere at such elevated temperatures. Such metals are commonly referred to as noble'metals and for the purposes of this specification include gold, silver, palladium, platinum, rhodium and iridium. However, this is not intended as an exclusive listing since other metals are known to have similar properties and may be used in the practice of the invention and are intendedto be included in the class of noble metals.

vided form or may be introduced as'large particles with the mixture being ground in a ball mill or similar apparatus to produce a finely ground mixture. It is preferred that the solid particles'in the mixture have a screen fineness of less than about 325 mesh. The particular liquid carrier utilized is not critical to the practice'of the invention and examples of suitable volatile carriers are toluol, xylol, oil, clear lacquer mixtures, isopropyl alcohol and even water. The mixture is applied to the base 111 to form the layer 10 by any suitable means such as brushing, spraying, stenciling or silk screening. The quantity of liquid carrier used in the mixture is selected to give the mixture the proper viscosity for the particular method used in applying the mixture to the base.

' After the layer has been applied to the base, the base and layer are preferably permitted to dry in circulating warm air for a short period. Then the base and layer are fired in a kiln which may be a conventional ceramic kiln,

preferably one utilizing electrical heat since such kilns produce a cleaner atmosphere.

The purpose of the firing operation is to solidify the glass into a continuous glass phase with the metal parmined in advance, since the heating characteristics of I individual kilns vary. The time and temperature cycle of the firing step is not otherwise critical and one skilled in the ceramic art can devise a number of suitable firing procedures.

The following is illustrative-of a suitable firing procedure. The base with the layer of resistance material is placed in the kiln and the temperature is increased to .1000" F. at a rate of approximately 400 F. per hour.

The temperature is then held at 1000 F- for about 30 minutes to insure the removal of all volatile and organic materials from the mixture and, also, to insure the uniform distribution of heat through the base and layer before the glass starts to fuse. .Then the temperature of the kiln is raised to 1490 F. at a rate of about 200 F. per hour. The temperature is maintained at the 1490 point for 30 minutes toinsure uniform heat distribution and at theend of this period, the kiln is allowed to cool .to room temperature by normal radiation. This particular firing cycle is used with a glass mixture consisting of 20% glass No. 1 and 80% glass No. 2 as described above. The firing cycle and temperature may be varied over a wide range as required fordifferent glass compo! sition and different kilns.

When the unit is cool, the layer of resistance material is firmly attached to the base and is in the form of a smooth black glossy layer retaining the exact configuration in which it had been applied to the base. Then electrodes and leads may be applied as previously described if desired, after which the component is ready for connection into an electrical circuit. It has been found that the introduction of fractional percentages or trace amounts of oneor more refractory metal oxides, commonly known as opacifiers, to the glass:

' metal mixture reduces the contact resistance between moving contacts and the surface of the solidified glassmetal mixture. When added in small percentages to-ceramic glasses, opacifiers have the property of being uniforinly dispersed. as colloidal particles or fiocs when the glass is melted and subsequently cooled,thereby producing a more uniform dispersion of metal particles throughout the resistancematerial when utilized in the invention. Examples of such opacifiers are tin oxide, antimony ox- The firing.

ide, zirconia, molybdenum oxide and chromium oxide. The layers of resistance material will range from a frac- Accordingly, although not essential to the performance of tion to a few thousandths of an inch in thickness with the the invention, it is preferred in the practice of the invenpreferred range being about DOGS-.003 inch. The matioll 10 include fractional P es of one or more of jority of the resistance elements being produced at the the opacifiers in the mixture of glass and metal, particu- 5 present time are in the order of one thousandth of an larly when the resistance element is to be used in a poinch thick. Since the resistance layer has a substantial tentiometer. thickness as compared to the sputtered and evaporated It has been found that the inclusion of a fractional metallic film resistors, thickness control is much less percentage of low melting temperature ceramic flux, such critical i the register of the invention, as bismuth OXide, molybdenum Oxide 0 Vanadium OXide 10 In the finished resistance element, amorphous metal in the glass-metal mixture produces adhesion of the metparticles are uniformly dispersed throughout the solidial particles to glass particles at temperatures below the fied glass forming a semi-conductive path through the softening point of the glass and tends to prevent agglomresistance material. The exact electrical phenomena eration of the metal particles as the firing temperature existing within the resistance material is not yet fully increases. Accordingly, although not essential to th known. However, it appears that the metal particles are performance of the invention, it is preferred in the pracspaced from each other or are slightly touching to protice of the invention to include a frctional percentage or duce a high resistance. It is known that an increase in trace amount of a low melting temperature ceramic flux percentage of metal in the mix produces a decrease in in the metal-glass mixture. over-all resistance which would be consistent with a re- The glass-metal mixture which constitutes a resistance duction in spacing between the metal particles and an material of the invention is predominantly glass with a increase in the number of particles which may be conrelatively small amount of metal. The particular protacting adjacent particles. It has been suggested that the portions utilized in a specific resistance element will deresistance of the layer is due to the fact that the particles pend upon the desired value of resistance. However, the are spaced apart less than the wavelength of an electron range of proportions in finished resistance elements will and that when the spacing between a majority of the parbe glass binder about 84-99 percent by weight and metal ticles exceeds this value, the layer will become a nonabout 1-16 percent by weight. The preferred range withconductor and when a majority of the metal particles in which most resistance elements of the invention fall are in contact with each other, the layer will become a is 91-98 percent by weight of glass and 2-9 percent by conductor having substantially zero resistance. weight of metal. The resistance characteristics of a par- In an alternative method of preparing the resistance ticular mixture are determined by manufacturing and material of the invention, the metal or metals may be testing a resistance element utilizing the mixture, after mixed with the finely ground glass binder with the metals which changes in resistance may be made by changing being in the form of soluble metal compounds which are the proportions used. decomposable by heat. Themetal compound or com- Various electrical characteristics of the resistance rnapounds are dissolved in a suitable solvent, such as in one terial may be controlled by using different noble metals of the essential oils, and thoroughly mixed or milled with and different mixtures of noble metals in the resistance the powdered glass to produce a uniform mixture. The material. The electrical characteristics of the metals volatile liquid carrier described in conjunction with the dispersed throughout the solidified glass tend to follow previously disclosed method is ordinarily not then re the electrical characteristics of the same metals when quired, since the solvent for the metal compounds serves used as solid metallic conductors. Alloys of platinum to make the mixture fluid and suitable for applying to and rhodium and gold and rhodium produce a lower the base. An important characteristic of such metal comrange of ohmic resistance values with positive temperapounds is that the metal is present in colloidal form so ture coeficients of resistivity. Gold, platinum and rhodithat when the base with the layer of resistance material um alloys produce low range ohmic resistance values applied thereto is fired to drive ofi the organic material with lower positive temperature coefficients of resistivity. present in the mixture, the metal compounds will be Gold, palladium and rhodium alloys produce a higher decomposed, leaving a residue of molecular size metal range of resistance values and these resistance values inparticles uniformly dispersed throughout the layer. It is crease with increasing percentages of palladium. The preferred to use metal-organic compounds such as metal temperature coeificients of resistivity range from low 'resinates or abietates as the soluble metal compounds positive to high negative values with increasing perdiscussed above.

centages of palladium. The addition of silver to these The metal oxides, such as bismuth oxide, tin oxide alloys will usually change the temperature coefficients of and chromium oxide, which are sometimes used in the resistivity to more negative values. resistance material of the invention, may also be intro- While innumerable combinations of materials may 5 duced into the mixture in the form of soluble metal combe used in making the resistance element of the invention, pounds as described in the preceding paragraph. Upon the following are set out as being illustrative of the range decomposition of the metal compounds, the metals will of mixtures which it is intended that this invention cover. be converted to oxides.

Mixture No. 1 2 3 4 5 6 7 8 9 10 Chromium Oxide I I I I058 I051 I050 I048 The configuration of the layer of resistance material In another embodiment of the method of preparing which is applied to the base will depend upon the resistthe resistance material of the invention, the resistance ance characteristic of the particular mixture employed material may be prepared in large'batches and stored inand upon the desired over-all resistance of the finished definitely to be used in making a desired number of reresistance element. As an illustration of the size of the sistance elements as required. In this method, the glass layer, the annular strip 10 of FIG. 1 may be made in the binder, metal or metals and metal oxides, if used, are order of one-half to one and one-half inches in diameter. mixed or milled together with the noble metals and the I '7 oxidizable metals being present in the form of soluble metal compounds. The mixing is carried out thoroughly so that each glass particle will be wet with the metal solutions. This mixture is gradually heated to approximately 700 F. being constantly stirred, to remove the volatiles and organic materials from the mixture, to decompose the metal compounds and to oxidize the oxidizable metals. The resulting dry material is ground to a fine powder and calcined at about 850 F. The resulting calcine is ground to a fine powder, preferably with all particles less than about 325 mesh, producing a dry material consisting of very small glass particles coated with an extremely thin layer of metal and metal oxide particles. This mixture may be stored indefinitely without change or deterioration and may be used in small portions to produce limited numbers of resistance element.

When it is desired to manufacture resistance elements using the material produced according to the preceding.

The base With the layer applied thereto is then firedto produce the continuous phase of solidified glass in the same manner as described above.

FIG; 2 illustrates another form of the resistance element of the invention in which a layer 15 of resistance material is applied to a rectangular base'ld and electrodes 17, 18 are then added at the ends of the layer 15. This form of the invention is particularly suitable for use in linear potentiometers,

In FIG. 3, a tube 20 serves as the base for a layer 21 of resistance material with cylindrical electrodes 22, 23 applied at the ends of the tube 20 overlying the ends of the tube and the layer 21. Flexible Wire leads 24, 25 are wrapped around and soldered to the electrodes 22, 23 respectively.

FIG. 4 shows a button-type fixed resistor having a layer of resistance material28 fired to a base 29 with electrodes 30, 31 fired to diametrically opposed portions of the layer 28 and flexible wire leads 32, 33 soldered to the electrodes 30, 31 respectively. The materials comprising the resistors of FIGS. 2, 3 and 4 and the methods of making the resistors are the same as described in conjunction with FIG. 1, the various resistors differing onlyin the physical shape of the finished product.

'to a high-temperature-resistant, electrically nonconducting base; heating the base and layer in an oxidizing atmospheretoa temperature below the melting point .of the glass; additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal; and cooling the layer to a hardened state- 3. A method of manufacturing an electrical resistance element including the steps of: forming a uniform mixture containing a finely ground glass and a solution of at least one noble metal-organic compound; heating the mixture to'reduce the metal-organic compound and to remove the volatiles and organic materials therein producing a dry mixture; grinding the dry mixture to a powder; heating the ground powder to produce calcination; grinding the calcined products to a fine powder; mixing the fine powder with a volatile liquid to form a viscous mixture; applying a layer of the viscous mixture to a high-temperatureresistant, electrically nonconducting base; heating the base and layer in an oxidizing atmosphere to a temperature below the melting point of the glass; additionally heating the, base and layer to a predetermined temperature at leastas high as the melting point of the glass but.

element including the steps of: forming a uniform mixture containing finely ground glass, a solution of at least one 7 noble metal resinate and a solution of a resinate of at Although exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

We claim as our invention:

1. In a method of manufacturing an electrical resistance element, the steps of: forming a mixture containing a finely ground glass and a solution of at least one noble metal-organic compound; applying a layer of the mixture to a high-temperature-resistant nonconducting base; heating the base and layer to an intermediate temperature to reduce the metal-organic compounds and to remove the volatiles and organic material therein; additionallyheating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such noble metal to produce a continuous glass phase having a smooth surface with the metal uniformly dispersed therethrough; and cooling the layer to a hardened state.

least one low melting temperature ceramic flux; heating the mixture to reduce the resinates and. to remove the violatilesand organic materials therein and to oxidize the flux to produce a dry mixture; grinding the drymixture to a powder; heating the ground powder to produce calcination; grinding the calcined products to a fine powder; mixing the fine powder with a volatile liquid to form a viscous mixture; applying a'layer of the viscous mixture to a,high-temperature-resistant, electrically nonconducting base; heating the base and layer in an oxidizing atmosphere to'a temperature below the melting point of the glass; additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal; and cooling the layer to a hardened state.

5. A method of manufacturing an electrical resistance element including the steps of: forming a uniform mixture containing a finely ground glass and a solution of at least one noble metal resinate, ta resinate of at least one low melting temperature ceramic flux, and at least one opacifier metal resinate; heating the mixture to reduce the resinates and to remove the volatiles and organic-materials therein and to oxidize the flux and opacifier metals producing a dry mixture, grinding the dry mixture to a powder; heating the ground powder to produce calcination; grinding the calcined products to a fine powder; mixing the fine powder with a volatile liquid to form a viscous mixture; applyinga layer'of the viscous mixture to a hightemperature-resistant, electrically non-conducting base;

heating the base and layer in an oxidizing atmosphere to a temperature below the melting point of the glass; additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal; and cooling the layer to a hardened state.

6. In a method of manufacturing an electrical resistance element, the steps of: forming a viscous mixture containing a volatile liquid carrier and powder-like particles of glass and at least one noble metal in the form of a noble metal-organic compound and having a melting point above that of saidglass; applying a uniform layer of the mixture to a high temperature resistant, electrically nonconducting base; heating the base and layer to a temperature below the melting point'of the glass to remove the volatile and organic materialtherein; and additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal.

7. In a method of manufacturing an electrical resistance element, the steps of: forming a viscous mixture containing a volatile liquid carrier and powder-like particles of glass and a solution of at least one noble metal organic compound in which said noble metal has a melting point above that of said glass; applying the mixture to a high temperature resistant, electrically nonconducting base to a uniform layer having a thickness of between about .0005 and 003 inch; heating the base and layer in an oxidizing atmosphere to a temperature below the melting point of the glass toremove the volatiles and organic material therein; and additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal to produce a continuous phase having a smooth, flat surface with the metal uniformly dispersed therethrough.

8. In a method of manufacturing an electrical re sistance element, the steps of: forming a viscous mixture containing a volatile liquid carrier and powder-like particles of glass and a solution of at least one noble metalorganic compound wherein said noble-metal has a melting point above that of said glass, the solid glass elements of said mixture including about 84-99 percent by weight of said glass and about 1-16 percent by weight of such metal; applying a uniform layer of the mixture to a high temperature resistant, electrically nonconduoting base; heating the base and layer to a temperature below the melting point of the glass to remove the volatile and organic material therein; and additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such metal.

9. The method defined in claim 8 including addition 10 to the viscous mixture of not more than 1 percent by weight of at least one low melting temperature ceramic flux.

10. The method defined in claim 8 including addition to the viscous mixture of not more than A2 percent by weight of at least one opacifier.

11. The method defined in claim 8 including addition to the viscous mixture of: not more than 1 percent by weight of at least one low melting temperature ceramic flux; and not more than /2 percent by weight of at least one opacifier.

12. In a method of manufacturing an electrical resistance element, the steps of: forming a mixture containing a finely ground glass and a solution of at least one noble metal resinate; applying a uniform layer of the mixture to a high temperature resistant nonconducting base; heating the base and layer to an intermediate temperature to reduce the metal resinate and to remove the volatiles and organic material therein; and additionally heating the base and layer to a predetermined temperature at least as high as the melting point of the glass but less than the melting point of such noble metal to produce a continuous glass phase having a smooth surface with the metal uniformly dispersed therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 2,461,878 Christensen et al Feb. 15, 1949 2,786,925 Kahan Mar. 26, 1957 2,837,487 Huttar June 3, 1958 2,950,996 Place et al Aug. 30, 1960 FOREIGN PATENTS 625,198 Great Britain June 23, 1949 155,250 Australia June 26, 1952 

1. IN A METHOD OF MANUFACTURING AN ELECTRICAL RESISTANCE ELEMENT, THE STEPS OF: FORMING A MIXTURE CONTAINING A FINELY GROUND GLASS AND A SOLUTION OF AT LEAST ONE NOBLE METAL-ORGANIC COMPOUND; APPLYING A LAYER OF THE MIXTURE TO A HIGH-TEMPERATURE-RESISTANT NONCONDUCTING BASE; HEATING THE BASE AND LAYER TO AN INTERMEDIATE TEMPERATURE TO REDUCE THE METAL-ORGANIC COMPOUNDS AND TO REMOVE THE VOLATILES AND ORGANIC MATERIAL THEREIN; ADDITIONALLY HEATING THE BASE AND LAYER TO A PREDETERMINED TEMPERTURE AT LEAST AS HIGH AS THE MELTING POINT OF THE GLASS BUT LESS THAN THE MELTING POINT OF SUCH NOBLE METAL TO PRODUCE A CONTINUOUS GLASS PHASE HAVING A SMOOTH SURFACE WITH THE METAL UNIFORMLY DISPERSED THERETHROUGH; AND COOLING THE LAYER TO A HARDENED STATE. 